In the beverage industry, it is known to fill non-carbonated beverages such as teas, juices, sports drinks, and other flavored beverages, into a plastic container or bottle at an elevated temperature (for example, at about 185° F. or 85° C.) in order to commercially sterilize the container's headspace and the beverage. This is commonly referred to as a hot-fill process.
However, after filling, sealing, and cooling the hot-filled bottle, an internal vacuum can force the bottle to collapse and deform. To mitigate this, hot-filled bottles have been provided with thicker side walls, special reinforcing structures, and/or special active bottle bases to compensate for these internal forces. The additional bottle material required to resist buckling increases weight and material cost compared to bottles for water or carbonated beverages. The design features required to mitigate the vacuum effects also impede bottle design freedom.
As the industry moves towards light-weighting of non-carbonated plastic bottles, top load resistance of the package is proportionately reduced which effectively lowers the permissible stack height during transport and warehousing of the product.
Another consideration when light-weighting bottles is the reduction in the sidewall thickness. Thinner sidewalls can increase the O2 permeation rate, thus accelerating product spoilage and reducing shelf life.
Several known solutions have been employed to help solve vacuum-related problems encountered during the hot-fill process.
For example, a commonly used technology is the implementation of vacuum panels positioned on the side of the bottle which are designed to move toward the center of the bottle after cooling. This sidewall movement displaces the volume within the bottle to compensate for the vacuum generated. The panels are ‘self-activated’ in that the vacuum within the container induces the panels to function. This technology has been successful for several years for the light-weighting of bottles. Some of these designs include conspicuously bulky panels that have hindered creativity by constraining design and have an effect on label placement. Other non-symmetric bottle designs that utilize vacuum panels have been less bulky, more aesthetically pleasing, and allow creative label placement. However, these non-symmetric bottles must be precisely designed which adds significant complexity and cost.
Another solution working along similar principles is the use of active base technology whereby the bottle has a specially-designed base that moves inwardly to displace the volume and compensate for vacuum. Some of these designs are self-activated, or utilize a mechanical piston to push up the base, or some combination of the two. With active base technology there are limitations to final shape geometry since vacuum compensation is limited to the available stroke or the upward movement of the base. If not designed precisely, the use of a piston to drive the base upward can also lead to package distortion which can constrain design freedom. Moreover, the implementation of a puck system at the bottling plant adds significant complexity and cost.
Another technology uses a specially processed base that is activated with heat. Heat causes the material to shrink and the surface of the bottle base is designed so that the shrinkage causes the base to move inward. The activation of this technology is through a machine which rapidly activates the base of the bottle with a heated plate and can also be assisted with a mechanical piston.
Yet another technology involves over-pressurizing the bottle to compensate for vacuum. This is accomplished by dosing the hot-filled bottle with liquid N2 prior to sealing the bottle. Upon dosing, the liquid N2 immediately transforms its state from a cryogenic liquid into a rapidly expanding nitrogen gas thereby pressurizing or charging the bottle after it is sealed. The resultant bottle is then under pressure rather than a vacuum. However, as a result of pressure generated within the container, as well as the large variation in final pressures, a petaloid or pressure-resistant base is required to be incorporated into the bottle design which can be objectionable to consumers. The large variation in final pressure occurs since the pressure is a function of dosage metering precision, distance or time to capping, as well as line smoothness as it relates to product spillage. In addition and most noticeably, the dosing and subsequent pressurization occur while the PET bottle is at its glass transition temperature (Tg). This can result in non-elastic deformation of the bottle and can lead to objectionably low fill points, and other bottle-shape irregularities.
In traditional liquid N2 dosing for water beverages (i.e. a cold-fill process since the water is bottled in a cold condition), the liquid N2 is dosed just prior to capping. While a large variation in final pressure occurs with this type of dosing process for the reasons discussed above, it is used to enhance package performance, in particular top load, since water bottles are quite thin and flimsy in an unpressurized state.
Still another technology involves incorporating a closure containing a pouch filled with an array of active ingredients that can generate N2 gas through an external energy source. After the bottle is filled and capped, and allowed to cool below its glass transition temperature (Tg), electromagnetic induction is externally activated. This starts the reaction which generates N2 within the headspace and compensates for vacuum. Another technology involves the use of absorber materials to relieve vacuum. However, these methods have not yet been proven to be commercially viable as they are cost prohibitive.
Known hot-filled bottles are heavy and are produced in the billions so a savings of several grams per bottle can amount to a substantial overall savings in material. As a result, it is in the interest of bottlers to reduce direct material costs, in particular for PET bottles. It is also in the interest of brand owners to reduce the amount of plastic that are used in their containers to heed public outcry for sustainability and other waste-reduction objectives.
Unfortunately, all of the above known technologies achieve limited weight savings and can restrict bottle design.
Accordingly, there exists a need for a system and method for significantly reducing the weight of hot-filled bottles while reducing the possibility of product spoilage, enhancing the evidence of tampering, imposing no bottle design constraints, eliminating observable low-fill height, and preventing bottle distortion.